Hydro Geophysical Investigation of Shebe Watershed, Jimma, South Western Ethiopia

Abstract

The need to prospect for additional ground water sources in Shebe watershed, Jimma, Shebe town water supply became inevitable because of the fact that the existed water supply and the quality of the water with current population and the population for the next

20 years is not enough and it must also be clean. The paper assesses Geological, Hydrogeophysical and groundwater potential site of Shebe watershed. Desk study, field study and geophysical survey were carried out with the objective of defining the most favorable location for borehole in shebe watershed. Survey specification and instruments used in this study work was latest instrument SAS 4000 resistivity meter with electrode spacing of AB/2=>750m and GPS. Data Analysis and interpretation has been done through different software such as Arc GIS, surfer, and GWW, IPI2win, & Global mapper. Thus implementation of sustainable potable water supply through source identification; how to supply safe/ potable water for the town; identification of recharge-discharge areas; depth to the water bearing zone; characterizing the aquifer using resistivity distribution were determined. The hydrogeological study revealed that the area consists of recent sediment deposits and volcanic rocks. Volcanic rocks are weathered and fractured which is suitable for groundwater abstraction through deep well drilling and whereas recent sediment deposits may be suitable for shallow groundwater abstraction. From both hydrogeophysical investigation VES1 andVES2 results, it was safely concluded that the target depth for well at Bake Qobo site1 of Shebe watershed should not be less than 140m & from the result of VES2 at the Bake Qobo site2, because the fifth layer is confined between the two aquifer layers, the optimum depth for the water bearing zone must not be less than 170m.